NITROGEN UPTAKE BY FUCUS SPIRALIS (PHAEOPHYCEAE)^1,²

<jats:title>ABSTRACT</jats:title><jats:p>Ammoniun, nitrate and nitrite update by <jats:italic>Fucus spiralis L.</jats:italic> from the Massachusetts coast was examined. Uptake of all appeared to follow saturation type nutrient uptake kinetics, with uptake often restricted at ambient nutrient concentrations. Although only relatively large difference in K<jats:sub>8</jats:sub> values could be easily distinguished, K<jats:sub>8</jats:sub> values for NO<jats:sub>3−</jats:sub> and NH<jats:sub>4+</jats:sub> were generally similar and low compared with NO<jats:sub>2−</jats:sub>. There was also some suggestion that K<jats:sub>8</jats:sub> was reduced at lower temperatures. At 15 C. V<jats:sub>max</jats:sub> for light and dark uptake for both NH<jats:sub>4</jats:sub>+ and NO<jats:sub>3−</jats:sub>, and light uptake of N0<jats:sub>2−</jats:sub> were similar, suggesting comparable potential use at higher concentrations. Ammonium and NO<jats:sub>3−</jats:sub>uptake decreased at lower temperatures giving Q<jats:sub>ro</jats:sub> values of 1.8 and 1.6, respectively, between 5 and 15°C. Nitrate and NH<jats:sub>4</jats:sub>+ were taken up together and high levels of NH<jats:sub>4</jats:sub>+ did not inhibit NO<jats:sub>3−</jats:sub> uptake. Light did not affect uptake of either but did stimulate NO<jats:sub>2−</jats:sub> uptake. Ammonium and NO<jats:sub>3−</jats:sub> uptake were highest in apical frond and whole young plants, and lowest in slower growing, older frond and stipe. On a relative basis. NO<jats:sub>3−</jats:sub>, NH<jats:sub>4+</jats:sub> and NO<jats:sub>2−</jats:sub> were estimated to have contributed ca. 59, 39 and 2% respectively, to the yearly N uptake by apical frond. During winter, NO<jats:sub>3−</jats:sub> would provide ca. twice the N to <jats:italic>F. spiralis</jats:italic> as would, NH<jats:sub>4</jats:sub>+. From summer to early fall, when NO<jats:sub>3−</jats:sub> levels are lower, NO<jats:sub>3−</jats:sub> and NH<jats:sub>4</jats:sub>+ would be used in comparable amounts.</jats:p>